The present invention relates to extrusion of non-fluorinated melt-processable polymers which contain fluoropolymer processing aids.
The melt extrusion of high molecular weight polymers, for example, hydrocarbon polymers and polyamides, into shaped structures such as tubing, pipe, wire coating or film is accomplished by well-known procedures wherein a rotating screw pushes a viscous polymer melt through an extruder barrel into a die in which the polymer is shaped to the desired form and is then subsequently cooled and solidified into a product having the general shape of the die.
In order to achieve low production costs, it is desirable to extrude the polymer at rapid rates. Higher extrusion rates may be readily obtained by increasing the rate of revolution of the extruder screw. However, this technique is subject to limitations imposed by the viscoelastic properties of the polymer substrate. Thus, at very high extrusion rates an unacceptable amount of thermal decomposition of the polymer can result. Further, extrudates having a rough surface are often obtained which can lead to formation of an undesirable pattern on the surface of the extrudate. These surface defects are also known as melt fracture. Extrusion at elevated temperatures obviates this problem but adds to processing costs. Also, cooling of the extrudate becomes problematic. In addition, if polyolefins are extruded at temperatures near their decomposition points, polymer degradation occurs.
It is desirable, therefore, to find highly efficient means of increasing the extrusion rate without raising the melt temperature, while producing articles having smooth surfaces. Changes in extruder and die configuration can improve polymer melt flow, but these modifications are not always practical or economically feasible. Another approach involves the addition of conventional wax-type process aids which reduce bulk viscosity and in some cases improve processing properties. However, the efficiency is marginal and the high levels of additive required often adversely affect other properties.
In Blatz, U.S. Pat. No. 3,125,547, it is disclosed that the use of 0.01-2.0 wt. % of a fluorocarbon polymer that is in a fluid state at the processing temperature (e.g. a fluoroelastomer) will reduce die pressure in extrusions of both high and low density polyethylenes, as well as other polyolefins. Further, use of this additive allows significant increase in extrusion rates without melt fracture.
Kamiya and Inui, in Japanese Examined Patent Application Kokoku 45-30574, cite the use of crystalline fluorocarbon polymers at temperatures below their melting points to eliminate die build-up, but they disclose nothing regarding other extrusion improvements.
Nishida, et al., in Japanese Patent Application Publication Kokai 62-64847, disclose injection molding compositions comprising a mixture of a) an ethylene/alpha olefin copolymer having a melt flow rate (MFR) of 0.2-200 g/10 minutes and a density of 0.850-0.945 g/cm3, with b) 0.001-1% by weight of a fluorinated hydrocarbon polymer having a fluorine to carbon ratio of at least 1:2.
Chu, in U.S. Pat. No. 4,740,341, discloses blends having improved extrudability comprising linear polymers of ethylene having incorporated therein small amounts of fluorocarbon polymers and polysiloxanes. The fluorocarbon polymers have fluorine to carbon ratios of at least 1:2 and are fluid at 120xc2x0-300xc2x0 C.
Larsen, in U.S. Pat. No. 3,334,157, discloses polyethylene which has been modified to improve its optical properties by incorporation of 0.015 to greater than 1.7% by wt., based on the mixture, of finely divided polytetrafluoroethylene.
More recently, improved fluoropolymer process aid compositions have been disclosed in for example, U.S. Pat. Nos. 4,855,360; 5,587,429 and 5,707,569. In these fluoropolymer process aid compositions, a second additive, such as a poly(oxyalkylene) or an ionomer resin, is introduced in order to improve extrusion processability of the non-fluorinated polymer.
In order to maximize processability improvements, the prior art has stated that it is desirable that the fluoropolymer process aid compositions be well dispersed in the non-fluorinated polymer which is to be extruded and that the smaller the particle size of the fluoropolymer, the better the dispersion and thus the better the processability. See, for example, xe2x80x9cDynamar(trademark) Polymer Processing Additive Optical Microscopy Method for Dispersion Analysis in Polyolefins xe2x80x9d (Dyneon 1997), which recommends uniform dispersions and fluoropolymer process aid particle sizes 2 microns or less in the extrudate; xe2x80x9cDynamar(trademark) Polymer Processing Additives Direct Addition During Resin Manufacture xe2x80x9d (Dyneon 12/2000), which recommends uniform dispersions and fluoropolymer process aid particle sizes of 3 microns or less in the extrudable composition. Similar recommendations have been made in U.S. Pat. Nos. 3,125,547; 5,010,130; and 6,048,939.
Due to these references which teach that extrusion processability is improved by improving the degree of the dispersion of the fluoropolymer process aid in the melt processable polymer, and by decreasing the particle size of the fluoropolymer, much of the prior work in this field has focused on improving the quality of the dispersion and minimizing the fluoropolymer particle size. Still, there is room for improvement in extrusion processability.
It has been surprising discovered that extrudable compositions which contain predominantly large particle size fluoropolymer actually process better, exhibiting fewer melt defects and have faster conditioning times, than those compositions which follow the recommendations of the prior art and strive for maximum fluoropolymer dispersion. By xe2x80x9cpredominantly large particle size fluoropolymerxe2x80x9d is meant a weight average particle size (as hereinafter defined) of greater than 2 microns, but less than 10 microns, as measured at a point immediately preceding the die. Extrudable compositions which contain predominantly large particle size fluoropolymer can be achieved by a number of means.
Accordingly, one aspect of the present invention is an extrudable composition for passing through a die, said composition comprising:
A) a non-fluorinated melt processable polymer; and
B) 25 to 2000 parts per million by weight, based on total weight of the extrudable composition, of fluoropolymer, said fluoropolymer having a weight average particle size greater than 2 microns and less than 10 microns, as measured at a point immediately preceding the die; and wherein said composition is substantially free of interfacial agent.
Another aspect of the present invention is an extrudable composition for passing through a die, said composition comprising:
A) a non-fluorinated melt processable polymer;
B) 25 to 2000 parts per million by weight, based on total weight of the extrudable composition, of a fluoropolymer, said fluoropolymer having a weight average particle size greater than 2 microns and less than 10 microns, as measured at a point immediately preceding the die; and
C) at least an effective amount of interfacial agent to achieve a fluoropolymer weight average particle size greater than 2 microns and less than 10 microns, as measured at a point immediately preceding the die, but no more than a 5:1 weight ratio of interfacial agent to fluoropolymer.
Another aspect of the instant invention is a process aid masterbatch comprising:
A) a non-fluorinated melt processable polymer;
B) 1 to 50 weight percent, based on total weight of the masterbatch, of fluoropolymer; and
C) at least an effective amount, to improve processability, of interfacial agent, but no more than a 5:1 weight ratio of interfacial agent to fluoropolymer, with the proviso that if the interfacial agent is a poly(oxyalkylene) polymer, it is present at less than a 1:1 weight ratio of poly(oxyalkylene) polymer to fluoropolymer.
The present invention is directed to means for improving the extrusion processability of non-fluorinated melt processable polymer compositions which contain fluoropolymer as a process aid. The term xe2x80x9cextrusion processabilityxe2x80x9d as used herein refers to the conditioning time (i.e. the elapsed time after extruder start up in which extruded articles exhibit a high degree of melt fracture before obtaining an extrudate having a smooth surface, free of melt fracture). Obviously, in order to minimize waste and reduce costs, a very short conditioning time is desirable.
Examples of non-fluorinated melt processable polymers include, but are not limited to, hydrocarbon resins, polyamides, chlorinated polyethylene, polyvinyl chloride, and polyesters. By the term xe2x80x9cnon-fluorinatedxe2x80x9d it is meant that the ratio of fluorine atoms to carbon atoms present in the polymer is less than 1:1. The non-fluorinated melt-processable polymers of this invention may be selected from a variety of polymer types. Such polymers include hydrocarbon polymers having melt indexes (measured according to ASTM D1238 at 190xc2x0 C., using a 2160 g weight) of 5.0 g/10 minutes or less, preferably 2.0 g/10 minutes or less. The hydrocarbon polymers may be elastomeric copolymers of ethylene, propylene, and optionally a non-conjugated diene monomer, for example 1,4-hexadiene. In general, hydrocarbon polymers also include any thermoplastic hydrocarbon polymer obtained by the homopolymerization or copolymerization of a monoolefin of the formula CH2xe2x95x90CHR, where R is H or an alkyl radical, usually of not more than eight carbon atoms. In particular, this invention is applicable to polyethylene, of both high density and low density, for example, polyethylenes having a density within the range 0.85 to 0.97 g/cm3; polypropylene; polybutene-1; poly(3-methylbutene); poly(methylpentene); and copolymers of ethylene and alpha-olefins such as propylene, butene-1, hexene-1, octene-1, decene-1, and octadecene. Hydrocarbon polymers may also include vinyl aromatic polymers such as polystyrene. Because specific hydrocarbon polymers exhibit differing melt characteristics, the practice of this invention may have greater utility in some hydrocarbon polymers than in others. Thus, hydrocarbon polymers such as polypropylene and branched polyethylene that are not of high molecular weight have favorable melt flow characteristics even at lower temperatures, so that surface roughness and other surface defects can be avoided by adjustment of extrusion conditions. These hydrocarbon polymers may only require the use of the fluorocarbon polymer extrusion aids and process of this invention under unusual and exacting extrusion conditions. However, other polymers such as high molecular weight, high density polyethylene, linear low density polyethylene copolymers, high molecular weight polypropylene, and propylene copolymers with other olefins, particularly those with narrow molecular weight distributions, do not permit this degree of freedom in variation of extrusion conditions. It is particularly with these resins that improvements in the surface quality of the extruded product are obtained with the compositions and process of this invention.
Other non-fluorinated melt-processable polymers that may be a component of the compositions of this invention include polyamides and polyesters. Specific examples of polyamides useful in the practice of this invention are nylon 6, nylon 6/6, nylon 6/10, nylon 11 and nylon 12. Suitable polyesters include poly(ethylene terephthalate) and poly(butylene terephthalate).
The fluoropolymers useful in the compositions of this invention include elastomeric fluoropolymers (i.e. fluoroelastomers or amorphous fluoropolymers) and thermoplastic fluoropolymers (i.e. semi-crystalline fluoropolymers). Fluoroelastomers useful in this invention are fluoropolymers that are normally in the fluid state at room temperature and above, i.e. fluoropolymers which have Tg values below room temperature and which exhibit little or no crystallinity at room temperature. It is preferred, but not essential, to employ fluoroelastomers having a fluorine to hydrogen ratio of at least 1:1.5. Fluorinated monomers which may be copolymerized to yield suitable fluoroelastomers include vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, tetrafluoroethylene and perfluoroalkyl perfluorovinyl ethers. Specific examples of the fluoroelastomers which may be employed include copolymers of vinylidene fluoride and a comonomer selected from hexafluoropropylene, chlorotrifluoroethylene, 1-hydropentafluoropropylene, and 2-hydropentafluoropropylene; copolymers of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene or 1- or 2-hydropentafluoropropylene; and copolymers of tetrafluoroethylene, propylene and, optionally, vinylidene fluoride, all of which are known in the art. In some cases these copolymers may also include bromine-containing comonomers as taught in Apotheker and Krusic, U.S. Pat. No. 4,035,565, or terminal iodo-groups, as taught in U.S. Pat. No. 4,243,770. The latter patent also discloses the use of iodo group-containing fluoroolefin comonomers. When fluorinated monomers are present in these copolymers in certain molar ratios, the glass transition temperature of the polymer is near or below 0xc2x0 C., and the compositions are useful elastomers that are readily available articles of commerce.
Semi-crystalline fluoropolymers which may be used in the invention include, but are not limited to poly(vinylidene fluoride), homopolymers and copolymers of tetrafluoroethylene (such as Teflon(copyright) FEP fluorocarbon resin, and copolymers of tetrafluoroethylene, propylene and, optionally, vinylidene fluoride).
Multimodal fluoropolymers, such as those disclosed in International Patent Publication WO 00/69967, may also be employed as the fluoropolymer in the compositions of this invention. By xe2x80x9cmultimodalxe2x80x9d is meant that the fluoropolymer has at least two components of discrete and different molecular weights. Both components may be amorphous or semi-crystalline, or one component may be amorphous and another component semi-crystalline.
If a single fluoropolymer is used in the compositions of this invention, the fluoropolymer must be substantially molten at the process temperature of the non-fluorinated host polymer. If a fluoropolymer blend is used, at least one of the blend components must meet this criterion. To function effectively as a process aid at weight average particle sizes as low as about 2 microns, an upper limit on the viscosity of the molten component of the process aid exists. If the molten component of the process aid is a fluoroelastomer, the Mooney viscosity (measured per ASTM-D1646 at 121xc2x0 C., large rotor, condition ML 1+10 minutes) must be 80 or less, preferably 60 to 80. If the molten component of the process aid is semi-crystalline, the melt index (ASTM D-1238, 265xc2x0 C., 5 kg weight) must be greater than 0.5 dg/min, preferably in the range 0.5 to 3 dg/min. Fluoropolymers become increasingly difficult to spread on the internal surfaces of process equipment as the fluoropolymer viscosity increases. Thus, beyond these viscosity limits, the process aid performance is degraded unless the weight average particle size of the fluoropolymer delivered to the die is extremely large, greater than about 10 microns. Fluoropolymer particles of this size are often large enough to form surface distortions or internal flaws in the extrudate. Therefore, it is desirable to restrict the weight average particle size of the fluoropolymer to less than 10 microns.
In the present invention it is desirable to control the weight average particle size of fluoropolymer process aid in the composition which is to be extruded so that it is greater than 2 microns, but less than 10 microns, when the composition reaches a point in the process immediately preceding the die (i.e. at the die entrance). Preferably, the weight average particle size of fluoropolymer is greater than 4 microns (and most preferably, greater than 6 microns) as measured just prior to the die.
Weight average particle size (diameter) is defined by the equation
A=(xcexa3iwiXi),
wherein A is weight average particle size (diameter); wi is the weight fraction of fluoropolymer particles in a particular sample having particle diameters in the range defined by Xi; and Xi is specified by dividing the particle diameter range in the sample into i intervals and assigning Xi to be the mean particle diameter of the range of particle sizes encompassed by the ith interval. Wi may be determined by a number of means including a) examining fluoropolymer dispersions using a light microscope, a digitizing camera, and a hot stage to melt the carrier resin, b) using a Confocal Laser microscope to image the fluoroelastomer particles in three dimensions, followed by size analysis using appropriate software c) analyzing photomicrographs of fluoropolymer dispersions, or d) by first dissolving the matrix resin, separating the fluoropolymer particles from matrix polymer resin, and then measuring particle size distribution by light scattering or some other known technique. When wi is calculated from photomicrographs, absent other knowledge to the contrary, the particles may be assumed to be substantially spherical in shape.
Although statistical moments of distributions are widely used in polymer science, these tools have not heretofore been applied to the field of fluoropolymer process aids. For example, in The Elements of Polymer Science and Engineering by Alfred Rudin (Academic Press, 1982) the number average molecular weight of a polymer is defined by the ratio of the first moment to the zeroth moment of the molecular weight distribution, while the weight average molecular weight is defined by the ratio of the second moment to the first moment of the molecular weight distribution. The number and weight averages correspond to the arithmetic mean of the number or weight distribution. Characterizing the fluoropolymer particle size distribution using a weight average rather than a number average is appropriate for the present invention, because, as described by Migler et al. (J. Rheol. 45(2), March/April 2001), fluoropolymer process aids function by depositing a fluoropolymer coating on internal die surfaces. Since the present invention is based on the discovery that, at equal fluoropolymer concentrations, large particles transfer fluoropolymer mass to the die surface more quickly than small particles, the salient quality of a particle distribution for process aids is a measure of where the majority of the fluoropolymer mass lies in the size distribution.
Furthermore, because statistical methods for particle size analysis have not been previously used in the field, prior references generally describe the fluoropolymer dispersion in terms of a size range. Unfortunately, a size range provides no information as to the weight average particle size of the distribution, other than indicating that the weight average must lie within the given range. A prior art extrudable composition that contains a minor amount of fluoropolymer particles greater than 2 microns in size, but having a majority of fluoropolymer particles less than 2 microns, would not provide the improvement in conditioning time seen with compositions of the present invention.
For ease of processing, fluoropolymer process aids are often in the form of a masterbatch, rather than neat, when they are added to the non-fluorinated melt processable polymer to form the composition which is to be extruded. A master batch is a dispersion (mixture) of fluoropolymer in a diluent polymer. The diluent polymer can be the same non-fluorinated melt-processable polymer that is to be extruded, or it can be a second non-fluorinated melt processable polymer that does not deleteriously affect the extrusion behavior of the first non-fluorinated melt processable polymer/process aid composition. Masterbatches typically contain 1-50 wt. % (preferably 1-30 wt. %) fluoropolymer processing aid (based on the total weight of the masterbatch). Masterbatches can be made, for example, by mixing the appropriate amount of fluoropolymer with diluent polymer in a mixer, such as a Banbury(copyright) mixer, at a temperature above the melting point of the non-fluorinated melt processable polymer, so as to form a masterbatch. Depending on masterbatch concentration, composition, and mixing conditions, the weight average particle size of fluoropolymer in a masterbatch of the prior art may be less than or greater than 2 microns. In preparing masterbatches that may be employed in the extrudable compositions of this invention, it is important to minimize exposure of the fluoropolymer to high shear, particularly for low fluoropolymer concentration masterbatches (i.e. those containing less than about 5 wt. % fluoropolymer). Otherwise, the weight average particle size of the fluoropolymer may be reduced to less than 2 microns in the masterbatch.
The rate at which a fluoropolymer process aid masterbatch is fed to an extruder is controlled so that the level of fluoropolymer in the resulting extrudable composition is between 25 to 2000 ppm (preferably 25 to 1000 ppm) by weight, based on the total weight of the extrudable composition.
There are several possible means for achieving the desirable fluoropolymer weight average particle size of greater than 2 microns, but less than 10 microns, as measured in the extrudable composition at a point near the die. One such means, an aspect of this invention, is a novel extrudable composition comprising a non-fluorinated melt processable polymer; and 25-2000 ppm by weight, based on the total weight of the extrudable composition, of fluoropolymer, wherein the fluoropolymer has a weight average particle size greater than 2 microns (preferably greater than 4 microns, most preferably greater than 6 microns), but less than 10 microns, as measured at a point immediately preceding the die (i.e. the die entrance). This extrudable composition is substantially free of interfacial agent (as hereinafter defined). By xe2x80x9csubstantially freexe2x80x9d is meant 0 to about 10 parts per million by weight interfacial agent, based on the total weight of the extrudable composition.
This extrudable composition of the invention may be made in a process wherein fluoropolymer (having a weight average particle size prior to introduction into the extruder of greater than 2 microns, preferably greater than 4 microns, most preferably greater than 6 microns) is introduced (either neat or in a masterbatch) to and mixed with non-fluorinated melt processable polymer to form an extrudable composition containing 25-2000 ppm fluoropolymer. Mixing the non-fluorinated polymer with the fluoropolymer, and pumping the resulting composition to the die, is performed in such a manner that the fluoropolymer is exposed to high shear for a minimal amount of time and thus, the fluoropolymer weight average particle size remains greater than 2 microns when the extrudable composition reaches the die entrance.
Care must be taken not to over process the extrudable composition containing the fluoropolymer before it reaches the die entrance. Otherwise, what may have started out as a large weight average particle size fluoropolymer when it was fed to the extruder, could be on the order of 1 micron (or less) when it reaches the die. Over processing includes any process wherein the fluoropolymer process aid is exposed to dispersive mixing conditions for too long. Over processing can take place in some types of polymer mixing devices such as fully intermeshing twin screw extruders, Buss Kneaders(copyright), single screw extruders equipped with screws which incorporate built in mixing devices (e.g. Maddock elements, pin mixers, ring elements, reverse flights), and single screw extruders having fine screen packs or restrictive dies that generate high pressure (i.e.  greater than 20 MPa) at the extruder exit. Preferably, processing will take place in a single screw extruder, with or without screw mounted mixing elements. Most preferably, screw mounted mixing elements and downstream mixing devices should be absent.
Because all extrusion processes may potentially degrade the fluoropolymer particle size, it is desirable to introduce the fluoropolymer to the extruder while in a particularly coarse state, such as a pellet, coarsely ground powder, or a masterbatch containing fluoropolymer particles having a weight average particle size much greater than 2 microns. To minimize dispersion and improve conditioning speed, the fluoropolymer viscosity at the extrusion processing conditions should be about equal to or greater than the viscosity of the non-fluorinated melt processable thermoplastic polymer. For example, a coarsely ground fluoropolymer may be dry blended at 25 ppm to 2000 ppm with a polyethylene resin, and fed to a single screw extruder. The extruder screw should have a low compression ratio (3:1 or less) and contain no mixing elements. Downstream of the screw, the polymer flow path should present minimal restrictions other than the die itself.
A preferred means in which to ensure that the weight average particle size of the fluoropolymer will be greater than 2 microns when it reaches the die is to introduce an interfacial agent into either the masterbatch or the extrudable composition. The interfacial agent somehow stabilizes the particle size of the fluoropolymer so that the fluoropolymer particles are less sensitive to high shear environments such as mixing. By xe2x80x9cinterfacial agentxe2x80x9d is meant a thermoplastic polymer which is characterized by 1) being in the liquid state (or molten) at the extrusion temperature, 2) having a lower melt viscosity than both the non-fluorinated melt processable polymer and fluoropolymer process aid, and 3) freely wets the surface of the fluoropolymer particles in the extrudable composition. Examples of such interfacial agents include, but are not limited to i) silicone-polyether copolymers; ii) aliphatic polyesters such as poly(butylene adipate), poly(lactic acid) and polycaprolactone polyesters (preferably, the polyester is not a block copolymer of a dicarboxylic acid with a poly(oxyalkylene) polymer); iii) aromatic polyesters such as phthalic acid diisobutyl ester; iv) polyether polyols (preferably, not a polyalkylene oxide) such as poly(tetramethylene ether glycol); v) amine oxides such as octyldimethyl amine oxide; vi) carboxylic acids such as hydroxy-butanedioic acid; vii) fatty acid esters such as sorbitan monolaurate and triglycerides; and viii) poly(oxyalkylene) polymers. As used herein, the term xe2x80x9cpoly(oxyalkylene) polymersxe2x80x9d refers to those polymers and their derivatives that are defined in U.S. Pat. No. 4,855,360. Such polymers include polyethylene glycols and their derivatives.
A preferred aliphatic polyester interfacial agent is a polycaprolactone having a number average molecular weight in the range 1000 to 32000, preferably 2000 to 10000, and most preferably 2000 to 4000.
The interfacial agent is a relatively low molecular weight ingredient which, for a particular system of fluoropolymer process aid and non-fluorinated melt processable polymer, preferentially locates at the interface between these two polymers. While not wishing to be bound by any particular explanation, it is believed that the interfacial agent functions by reducing the shear stress on the fluoropolymer particles during melt processing of the non-fluorinated polymer, thereby reducing the ability of melt processing equipment to affect the dispersion of the fluoropolymer. The interfacial agent may be introduced to the mixture of fluoropolymer and non-fluorinated polymer at any point up to and including the final melt shaping process, with the proviso that at the point of introduction, the weight average particle size of fluoropolymer particles must be greater than 2 microns. It is most desirable to combine the fluoropolymer and interfacial agent in a masterbatching step where both ingredients are present at high concentration (i.e. at greater than or equal to 1 wt. %, based on the total weight of masterbatch), so that the wetting of the fluoropolymer surface in the mixture occurs quickly.
Accordingly, another aspect of the invention is a masterbatch comprising a) non-fluorinated melt processable polymer; b) 1 to 50 weight percent, based on the total weight of the masterbatch, of fluoropolymer; and c) at least an effective amount of an interfacial agent to improve processability. By xe2x80x9cat least an effective amountxe2x80x9d is defined as any amount of interfacial agent present in the masterbatch which, when the masterbatch is mixed with a non-fluorinated melt processable polymer, results in an extrudable composition that provides a measurable reduction in conditioning time for removal of all surface melt fracture during extrusion, as compared to the same composition not containing interfacial agent. Generally, there is no benefit in extrusion processability by incorporating into the masterbatch more interfacial agent than 5 times the level of that of the fluoropolymer process aid (i.e. a weight ratio of interfacial agent to fluoropolymer up to 5:1 in the composition). If the interfacial agent is a poly(oxyalkylene) polymer, preferably the weight ratio of interfacial agent to fluoropolymer is less than 1:1 in the masterbatch.
Another aspect of the present invention is a composition comprising a) fluoropolymer and b) polycaprolactone. Such a blend may be utilized in the manufacture of masterbatches, or as an additive to be introduced directly into an extrudable composition. Preferably, the weight ratio of polycaprolactone to fluoropolymer is no greater than 5:1 in this composition. Preferably, the polycaprolactone employed in this aspect of the invention has a number average molecular weight in the range 1000 to 32000, more preferably 2000 to 10000, and most preferably 2000 to 4000. These blends may be made by a variety of methods including admixing pellets or powders of fluoropolymer and polycaprolactone, or encapsulating fluoropolymer granules with a coating of polycaprolactone.
Another aspect of the present invention is an extrudable composition for passing through a die, said composition comprising a) non-fluorinated melt processable polymer; b) 25 to 2000 ppm by weight, based on the total weight of the extrudable composition, of fluoropolymer, said fluoropolymer having a weight average particle size (as measured at a point immediately preceding the die) of greater than 2 microns (preferably greater than 4 microns, most preferably greater than 6 microns), but less than 10 microns; and c) at least an effective amount of an interfacial agent to achieve a weight average fluoropolymer particle size greater than 2 microns, but less than 10 microns, as measured at a point immediately preceding the die. The upper level of interfacial agent present in the extrudable composition is a weight ratio of interfacial agent to fluoropolymer of 5:1, and, preferably, the latter ratio is less than 1:1 when the interfacial agent is a poly(oxyalkylene) polymer.
The compositions of the invention are particularly useful in extrusions of melt processable polyolefins. Such extrusion processes are commonly used in manufacture of blown films and wire and cable jacketing.